1. Field of the Invention
The present invention concerns a lightweight, insulating, stitch bonded nonwoven fabric and a process for making it.
2. Description of the Prior Art
Stitchbonded fabrics, made on multi-needle stitching machines, are known in the art. Three of my earlier patents, U.S. Pat. Nos. 4,704,321, 4,737,394 and 4,773,238, disclose a variety of such fabrics, wherein the stitch-bonding preferably is performed with an elastic stitching thread and a "substantially nonbonded" fibrous material.
U.S. Pat. No. 4,704,321 discloses multi-needle stitiching a substantially nonbonded fibrous layer of polyethylene plexifilamentary film-fibril strands with elastic thread under tension and then releasing the tension to cause the fibrous layer to contract or pucker. Spandex elastomeric yarns, which can elongate and retract in the range of 100 to 250%, are preferred for the stitching thread. Stitching threads of heat shrinkable yarns, textured yarns, stretch yarns of polyester or nylon, among others, also are disclosed. The latter yarns are said to function in a similar manner to spandex yarns but with considerably less elongation and contraction. The stitchbonded product preferably has a final contracted area that is in the range of 70 to 35% of the original area of the fibrous layer and is particularly suited for use as a wipe-cloth.
U.S. Pat. No. 4,737,394 discloses the stitchbonding of a fibrous polyolefin layer, preferably with a spandex thread (as in U.S. Pat. No. 4,704,321) to form the outer porous fabric of an oil-absorbing article.
U.S. Pat. No. 4,773,238 discloses stitchbonding of a substantially nonbonded layer of textile-decitex fibers with an elastic stitching thread to cause the fibrous layer to become "gathered" between the stitches and rows of stitches. Preferably, the amount of gathering provides the resultant product with an area that is no more than 40% the original area of the fibrous layer. The large reduction in area is provided preferably by spandex yarns that are under sufficient tension to elongate 100 to 250% while stitching through the fibrous layer and then having the tension released after the stitching is completed. "Substantially nonbonded", with regard to the layer of textile decitex fibers, is said to mean that the fibers generally are not bonded to each other, by for example chemical or thermal action. However, a small amount of point bonding or line bonding is included in the term "substantially nonbonded", as long as the bonding is not sufficient to prevent the fibrous layer from contracting or gathering after having been stitched with the elastic thread. The resultant product is disclosed to be an excellent dust cloth and also suitable for use in thin insulative gloves, thermal underwear blankets and the like.
Although the above-described stitchbonded fabrics have performed satisfactorily in several end-uses, their utility as insulating fabrics could be enhanced greatly, especially if significant increases could be made in the specific volume of the fabrics and in their resistance to deterioration by repeated washing. Also, if the high elongations used with the favored elastic stitching yarns of the above-described processes could be avoided, more efficient and better control could be achieved in the stitch-bonding operation.
An object of the present invention is to provide an improved stitchbonded insulating fabric and a process for making it. Surprisingly, as described below, these purposes are achieved by stitchbonding a thin layer of bonded fibers in a way that reduces the area of the layer very little while significantly increasing the thickness of the layer, as compared to the earlier processes described above.